1. Field of the Invention
The present invention relates to a technique of radio transmission and reception of frequency hopping system for performing communication while switching a carrier frequency, more particularly, to a radio transceiver of Ultra Wide Band (UWB) system and an IC in which the signal bandwidth of one frequency band is 528 MHz, namely a wide band (ultra wide band).
2. Related Art
In a wireless local area network (wireless LAN), a system which configures the frequency band of wide band signal using multi-carrier system to make the transmission speed faster and implements frequency hopping of the frequency bands at high speed to spread the signal spectrum has been proposed.
Specifically, the Ultra Wide band (UWB) system using orthogonal frequency division multiplexing (OFDM) for the multi-carrier system has been proposed in the IEEE 802.15a standard of the United States. This UWB is referred to as Multi-band OFDM (MB-OFDM) in Multi-Band OFDM Alliance (MBOA) and is being reviewed for standardization.
The main points of the MB-OFDM technical standard are as follows. (1) The band center frequency interval is Fstep=528 MHz, and includes three bands of 3432 MHz, 3960 MHz, and 4488 MHz in 4 GHz band, and four bands of 6336 MHz, 6864 MHz, 7128 MHz and 7392 MHz in 7 GHz band. (2) These bands are frequency hopped in a frequency transition period of Ttj<9.0 nsec. Accordingly, the radio signal in which the transmission rate is high and the spectrum is spread in ultra wide band is realized.
A conventional art of a frequency oscillator used in this type of UWB transceiver is disclosed in “A 3.1 to 8.2 GHz Direct Conversion Receiver for MB-OFDM UWB Communications, A. Ismail, A. Abidi, 2005 IEEE International Solid-State Circuits Conference, Session 11, 11.5” (Non-patent Document 1) made public in International Solid-State Circuit Conference held on February, 2005 under the auspices of IEEE. This conventional art includes a frequency oscillator, a plurality of frequency dividers, a frequency mixer, and a switchable buffer amplifier, where the signal of abovesaid (1) is frequency transitioned within 9 nsec by repeating addition and subtraction of signals and thereafter, switching to a specific signal and outputting the same.
The conventional art has drawbacks in that: (1) the hopping frequency obtained in the oscillator is a fixed frequency and thus does not have degree of freedom in terms of communication system; and (2) a radio frequency oscillator of 16 GHz is required.
On the contrary, frequency oscillators used in a radio transceiver includes: (1) a frequency synthesizer; and (2) a direct digital synthesizer (DDS). The system of (1) is a system of configuring a phase locked loop (PLL) by: a voltage control oscillator (VCO); a phase comparator; and a programmable divider, and obtaining the target frequency. The system of (2) is a system of obtaining a frequency set by outputting data to a digital/analog converter (DAC) from a numeral controlled oscillator (NCO), which is a ROM storing sine waves.
The conventional art related to the DDS is disclosed in Japanese Patent Application Laid-Open Publication No. 2000-332539 (Patent Document 1).
When considering applications of the DDS to a frequency hopping system of wide band such as MB-OFDM, there were problems in that: (1) a carrier frequency transition of wide band (e.g., 528 MHz) cannot be performed; and (2) the carrier frequency cannot be switched at high speed.
Other techniques of radio communication system, for example, the radio property specification and Layer 1 specification of the WCDMA system are respectively defined in “Technical Specification Group Radio Access Networks; UE radio transmission and reception (FDD) (Release 7), 3GPP TS 25.101 v7.0.0 (2005-06), URL: www.3gpp.org/specs/specs.htm” (Non-patent Document 2) and “Technical Specification Group Radio Access Networks; Physical layer procedures (FDD) (Release 6), 3GPP TS 25.214 v6.3.0 (2004-09), URL: www.3gpp.org/specs/specs.htm” (Non-patent Document 3), released by the 3GPP.